1. Field of the Invention
The present invention relates to a driving apparatus for a matrix panel used in a monitor of a television receiver, a computer, etc., and an image display apparatus provided with the same. In particular, the invention relates to a driving apparatus for a matrix panel in which modulation elements such as semiconductor light emitting elements and electron emitting elements are arranged at intersections of a matrix, a driver circuit thereof, and an image display apparatus provided with the same.
2. Description of the Related Art
First, a description will be given of the electron emitting element as an example of the modulation element. FIG. 31 schematically shows a matrix panel used for a display apparatus etc.
In FIG. 31, an electron emitting element 1 is schematically shown as an example of the modulation element. A column wiring 2 and a row wiring 3 have wiring resistances 4 and 5 respectively according to a specific resistance of components or size of the wirings. Note that, for simplicity in illustration, a matrix having a size of 4×4 elements is adopted here. Needless to say, however, a matrix size is not limited to this. For example, in a case of using a multi-electron beam source for an image display apparatus, enough elements to achieve a desired image display may be arranged and wired.
In the multi-electron beam source in which the electron emitting elements are wired in passive matrix, electric signals are appropriately applied to the row and column wirings in order to output the desired electron beam.
FIG. 32 shows a column wiring drive waveform and a row wiring drive waveform of signals applied to the matrix panel. For example, in order to drive the electron emitting elements in any one of the rows in the matrix, a row selection signal having a selection voltage Vs is applied to the row wiring of the row to be selected, while a non-selection voltage Vns is applied to the row wiring in a non-selection state. In synchronization therewith, a drive voltage Ve is applied to the column wiring for a given time period in order to output the electron beam.
According to the above method, the voltage corresponding to Ve-Vs is applied to the electron emitting element in the row to be selected. On the other hand, the voltage corresponding to Ve-Vns is applied to the electron emitting element in the row in the non-selection state. If the voltages Ve, Vs, and Vns are set to an appropriate level based on an electron emission threshold of the electron emitting element, the electron emitting elements in the row to be selected may solely output the electron beam with the desired intensity. Also, a cold-cathode element exhibits high-speed response. Thus, by changing the length of period for which the drive voltage Ve is applied, that is, a pulse width of the voltage Ve as indicated by the arrow of FIG. 32, the length of period for which the electron beam is outputted can be changed.
Further, with a modulation system of controlling luminescence by changing a voltage amplitude to be applied to the column wiring and a current value therefore, the output of the electron beam can be controlled as well.
In the above example, the matrix having 4×4 elements has been described. However, for the image display apparatus that displays a television image in actuality, for example, in a case of VGA (video graphics array), the matrix having 640 (horizontal lines)×480 (vertical lines) elements is required. Considering a color image display, horizontal lines three times more than the 640 lines are required, i.e., the matrix having 1920 (horizontal lines)×480 (vertical lines) elements is required.
For example, assuming that the current flowing into the electron beam source becomes 1 mA, the current of 1 mA is required for driving the column wiring. On the other hand, the current required for driving the row wiring corresponds to 1 mA×1920=1.92 A since the current is caused to flow there into from all the column wirings. Therefore, a row wiring driver that drives the row wiring should have a current drive power of several A.
When considering the VGA by way of example, the row wiring driver has the outputs as many as 480 channels and thus, high costs are involved when the driver is constructed by discrete devices. Therefore, in many cases, it is incorporated into an IC. However, taking into consideration the driving of current with several amperes, it is required for an output buffer to have a low ON resistance.
Examples of a method of reducing the ON resistance of the output buffer in the IC include a method of increasing an IC chip area. In the case of increasing the chip area, for example, a high withstand voltage MOS should have a double diffusion structure and an occupied area of chip increases. When the output ON resistance (Ron) of 100 mΩ is supposedly needed, the chip occupies the area of about 1 mm2.
Accordingly, assuming the IC having the output of 80 channels, the output buffer solely occupies the area of 80 mm2. Further, in order to drive the output buffer, a pre-buffer is necessary. Actually, the chip area of substantially 100 mm2 required only for the output buffer.
As described above, in order to decrease the resistance of the output buffer of the IC, the chip area should be increased. As a result, the number of chips that can be obtained from one wafer decreases, so that unit cost per chip increases. In particular, this largely affects the IC with the multiple outputs.
As a countermeasure against the above-mentioned problems, the inventors of the present invention have made intensive studies on a correction circuit that corrects variations of the voltage in order to suppress the voltage variation due to the ON resistance of the row driver circuit. However, the inventors have found that only the application of the correction circuit is insufficient to cope with the problems.
For example, if the column wiring is driven with simple pulse width modulation (PWM) along with the correction circuit, according to information on gradation to be displayed through pixels in the one row, the current flowing into the row wirings abruptly changes during one horizontal scanning period. Thus, the influence of response characteristics of the correction circuit may be exerted more consciously.
Also, due to the resistance at a connection portion where the modulation element is electrically connected with the driver circuit as well, an effective drive voltage actually applied to the modulation element may decrease beyond an allowable range.